The present invention relates to a mixture which is polymerizable by radiation, particularly by light, and which comprises as essential constituents: a polymeric binder, a polymerization initiator which can be activated by radiation, and a free radical polymerizable acrylate or methacrylate of a polyhydric hydroxy compound having at least two urethane groups in the molecule.
Mixtures of this type are known and are primarily used for preparing radiation-sensitive, particularly light-sensitive, recording materials. Such materials are used, for example, for preparing printing plates, photoresists and relief images.
German Offenlegungsschrift No. 2,064,079 describes photopolymerizable mixtures which contain polymerizable reaction products of diisocyanates with acrylates or methacrylates of polyhydric alcohols containing at least one further free hydroxy group, e.g. hydroxyethyl methacrylate. These mixtures tend to form relatively brittle light-hardened products. They also have a limited shelf life, since the monomers have a significant vapor pressure even at only slightly elevated temperatures.
German Offenlegungsschrift No. 2,361,041 describes mixtures containing similar polymerizable compounds which have more than two urethane groups and also polyether units in the molecule. These mixtures produce only a limited crosslink density, and are relatively sensitive to atmospheric oxygen.
German Offenlegungsschrift No. 2,822,190 describes mixtures comprising high molecular weight monomers containing urethane groups which have many advantages for certain purposes, for example for the preparation of dry transferrable photoresist layers. However, even these mixtures produce products with limited crosslink densities because of their lower content of polymerizable groups per molecular weight unit.
Similar polymerizable oligourethanes are described in U.S. Pat. Nos. 3,850,770 and 4,198,238 and in European Published Application No. 9,967.
Although light-sensitive or radiation-sensitive recording materials prepared with such polymerizable compounds exhibit a number of outstanding properties, these properties are accompanied, in most cases, by certain disadvantages. Thus, although the higher molecular weight oligourethanes containing polyether groups give layers with outstanding mechanical properties in the exposed and unexposed states, the crosslink density achieved with these substances is lower than in the case of certain low molecular weight monomers. Many monomers also produce tacky layers, particularly in combination with the preferred binding agents which can be developed in aqueous alkaline media. Further, the sensitivity of most of the known materials to atmospheric oxygen is greater than is desirable.